Traditionally, cell counting is performed by mixing an aliquot of a population of cells with trypan blue dye and counting cells disposed on a hemocytometer stage using a microscope. The viable cell density is then determined by visual counting methods. Such hemocytometer techniques are error-prone and require a manual sample of the bioreactor contents. Consequently, a number of alternate analytical techniques have been developed, including techniques that count cells based on electrical impedance as well as techniques that use trypan blue exclusion.
Dielectric spectroscopy (DS) techniques measure the electrical impedance of a sample by applying a time-varying signal to the sample via electrodes. DS techniques can provide information about cell structure and properties, including intracellular contents, membrane shape and polarizability, and other cellular properties.
The dielectric properties of biological cells can provide information regarding the cellular and molecular state of a given population of cells. The dielectric properties of biological cells are mainly characterized by the beta-dispersion, a dielectric relaxation phenomenon, which is observed in the medium and high frequency (HF) range of the radio spectrum. The beta-dispersion mechanism is due to Maxwell-Wagner polarization (interfacial polarization) at the external and internal interfaces of the phospholipid membrane, and is caused by the ability of biological cell membranes to impede electrical current. Additional contributions to the beta-dispersion may be observed due to the presence of organelles, heterogeneity of the cell population, and other phenomena.
DS techniques to estimate dielectric properties of biological cells are discussed at, for example, U.S. Pat. Nos. 4,810,650, 4,965,206, 6,496,020, 6,596,507, and 7,930,110. In the known techniques to estimate biological property data, electrical property data are received by applying a signal to a solution of cells across multiple frequencies.
A need exists for non-destructive screening techniques to associate physical cell-specific phenomena with cell and molecular biology phenomena. Cell-based screening is a powerful method that uses living cells to test the effect of different nutrients, toxicants, and environmental factors on the cellular and molecular phenotype of cells. Thus, there is ample opportunity for the development of tools that permit systematic prediction of cell viability characteristics.